A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a navigation function is provided in a vehicle. Such a navigation system detects the position of the user, and reads out map data pertaining to an area at the current position of the user from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Alternatively, such map data can be provided to the navigation system from a remote server through a communication network such as Internet.
Typically, the navigation system displays a map image on a monitor screen while superposing a mark representing the current location of the user on the map image. When a destination is set, the navigation system determines a route to the destination and starts a route guidance function to guide the user to the destination. To determine the route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters.
An example of operation of the navigation system is described with reference to display examples of FIGS. 1A-1H. FIG. 1A shows an example of map screen when the destination is not specified. Typically, the navigation system displays a map image on which the vehicle (vehicle position VP) is running and a name of the street. When selecting a “Destination” menu on a main menu screen (not shown), the navigation system displays an “Find Destination By” screen as shown in FIG. 1B for specifying an input method for selecting the destination. The screen lists various methods for selecting the destination.
When selecting, for example, a “Point of Interest” method in FIG. 1B, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1C. If the “Place Type” is selected in FIG. 1C, the navigation system shows an “Select Category” screen such as shown in FIG. 1D. When the user selects a specific category “Restaurant”, the navigation system retrieves POIs in the selected category as shown in FIG. 1E.
If the user selects a particular restaurant from the list, the navigation system displays a “Confirm Route” screen as shown in FIG. 1F. In this example, the “Confirm Route” screen lists the name, address and phone number of the destination (POI specified by the user). If this is the correct destination, the user enters an “OK to Proceed” key to proceed to the next procedure.
In FIG. 1G, the navigation system calculates and determines a route to the destination. The navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. After determining the calculated route, the navigation system starts the route guidance operation as shown in FIG. 1H to guide the user along the calculated route to the destination.
The navigation system will determine an optimum route by calculating the route that is regarded as the most efficient in terms of cost such as a distance, time, type of road, fee, etc. In a case where a distance for a particular route is long, the cost associated with the route is deemed high. Even a distance is short, if it takes a long time to pass through a particular route, the cost associated with the route is deemed high. If a particular route includes a toll road, the cost associated with the route is deemed high.
Some recent navigation systems are equipped with a function that can receive traffic information such as traffic incidents and conditions of roads. When the existence of a traffic incident is indicated in a particular road, the cost for the road is high. As a result, the road having the traffic incident becomes less likely to be chosen as a desired route to the destination. However, when there are conflicting information for such a road, how to weigh the cost in calculating the route is problematic.
Such a situation is explained with reference to the schematic view of FIG. 2 showing a map image reflecting traffic incident information thereon. In this example, possible routes include a route taking Freeway 5. A traffic incident icon 61 indicates that there is a traffic incident on Freeway 5. In FIG. 2, assuming also that the traffic flow information indicates reasonably free flows of traffic, for example, 50 miles per hour. Thus, there is a conflict as to which information represent the actual road condition and how to weigh the information for calculating the cost.
Moreover, there is also a case where one route contains traffic information whereas an alternative route does not contain traffic information. An example of such a situation is shown in FIG. 3 in which possible routes include Freeway 8 and Freeway 52. Freeway 8 has the traffic flow information (20 miles/hour) whereas Freeway 52 does not. The traffic speed on Freeway 52 is therefore unknown, and thus, how the cost associated with the route involving Freeway 52 and Freeway 8 is to be evaluated is problematic in finding an optimum route. Accordingly, there is a need of a method to evaluate the reliability and accuracy of the traffic information to obtain an optimum route to the destination.